netdev - Re: [PATCH v3 1/2] net: stmmac: make sure that ptp_rate is not 0 before configuring timestamping

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Message-Id: <DA7NLJ1CKSFM.3FWBC90NACTRV@bootlin.com>
Date: Wed, 28 May 2025 10:33:46 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: Alexis Lothoré <alexis.lothore@...tlin.com>, "Alexandre
 Torgue" <alexandre.torgue@...s.st.com>, "Jose Abreu"
 <joabreu@...opsys.com>, "Andrew Lunn" <andrew+netdev@...n.ch>, "David S.
 Miller" <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>, "Maxime
 Coquelin" <mcoquelin.stm32@...il.com>, "Richard Cochran"
 <richardcochran@...il.com>, "Phil Reid" <preid@...ctromag.com.au>
Cc: "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>, "Maxime Chevallier"
 <maxime.chevallier@...tlin.com>, <netdev@...r.kernel.org>,
 <linux-stm32@...md-mailman.stormreply.com>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
 "Jose Abreu" <Jose.Abreu@...opsys.com>
Subject: Re: [PATCH v3 1/2] net: stmmac: make sure that ptp_rate is not 0
 before configuring timestamping

On Wed May 28, 2025 at 10:29 AM CEST, Alexis Lothoré wrote:
> The stmmac platform drivers that do not open-code the clk_ptp_rate value
> after having retrieved the default one from the device-tree can end up
> with 0 in clk_ptp_rate (as clk_get_rate can return 0). It will
> eventually propagate up to PTP initialization when bringing up the
> interface, leading to a divide by 0:
>
>  Division by zero in kernel.
>  CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.30-00001-g48313bd5768a #22
>  Hardware name: STM32 (Device Tree Support)
>  Call trace:
>   unwind_backtrace from show_stack+0x18/0x1c
>   show_stack from dump_stack_lvl+0x6c/0x8c
>   dump_stack_lvl from Ldiv0_64+0x8/0x18
>   Ldiv0_64 from stmmac_init_tstamp_counter+0x190/0x1a4
>   stmmac_init_tstamp_counter from stmmac_hw_setup+0xc1c/0x111c
>   stmmac_hw_setup from __stmmac_open+0x18c/0x434
>   __stmmac_open from stmmac_open+0x3c/0xbc
>   stmmac_open from __dev_open+0xf4/0x1ac
>   __dev_open from __dev_change_flags+0x1cc/0x224
>   __dev_change_flags from dev_change_flags+0x24/0x60
>   dev_change_flags from ip_auto_config+0x2e8/0x11a0
>   ip_auto_config from do_one_initcall+0x84/0x33c
>   do_one_initcall from kernel_init_freeable+0x1b8/0x214
>   kernel_init_freeable from kernel_init+0x24/0x140
>   kernel_init from ret_from_fork+0x14/0x28
>  Exception stack(0xe0815fb0 to 0xe0815ff8)
>
> Prevent this division by 0 by adding an explicit check and error log
> about the actual issue. While at it, remove the same check from
> stmmac_ptp_register, which then becomes duplicate
>
> Fixes: 19d857c9038e ("stmmac: Fix calculations for ptp counters when clock input = 50Mhz.")
> Signed-off-by: Alexis Lothoré <alexis.lothore@...tlin.com>

I realize that I forgot to collect Yanteng's and Maxime's RB on this patch,
and I guess they remain relevant despite the second new patch, my bad. I'll
remember to add them if this needs a new revision.

Alexis

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com